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Mercury  Venus  Earth  Mars  Jupiter  Saturn  Uranus  Neptune  Pluto


According to the classification based on size, Pluto is one of the small planets. The other four small planets are Mercury, Venus, Earth and Mars. These planets all have diameters less than 13000 kilometers.

The other four planets, Jupiter, Saturn, Uranus and Neptune are known as the giant planets or the gas giants. These planets have diameters greater than 48000 kilometers.

Under the system which classifies planets as “inner planets” and “outer planets”, according to their distance from the Sun, Pluto would be grouped with the gas giants as an outer planet.

Where is It?
Pluto is the ninth, or last, planet in the solar system. The orbit, or path the planet takes around our Sun is an ellipse, or stretched out circle. For this reason there are times when Pluto is the planet furthest away from the Sun. There are also times when it is closer to the Sun than Neptune.

Pluto is a very long way from the Sun. Its average distance from the Sun is over 6 billion kilometers. The closest Pluto gets to the Sun is over 4.3 billion kilometers., and the furthest away it gets is over 7.2 billion kilometers. From Pluto, the Sun is not much brighter than any other star.

How Did It Get Its Name?
Pluto is the Roman god of darkness and the underworld. Perhaps Pluto got its name because it is always in darkness. It may have also have been given its name from the fact that its symbol “PL” are the initials of Percival Lowell, who founded the observatory where Pluto’s discoverer, Mr. Tombaugh, worked.

How long are its years and days?
A year on Pluto lasts for 248 Earth years. A day on Pluto, is over six Earth days.

How Big Is It?
Pluto is the smallest planet in our solar system at a little over 2080 kilometers. in diameter, or about one-sixth the diameter of Earth. If Earth was the size of a soccer ball, Pluto would be the size of a ping-pong ball. Many of the moons of other planets, including the Earth’s Moon, are larger than Pluto.

Can It Be Seen From Earth?
Pluto cannot be seen even with a normal telescope. Pluto is so tiny, and so far away, that a telescope at least 25 centimeters in diameter is needed to see it. It might be possible to see Pluto through the telescope at a nearby observatory. Even through that telescope, Pluto is nothing more than a pinpoint of light among the stars.

What Is It Made Of?
Pluto is the only planet in the solar system that has not been explored with a spacecraft. What is know about the dark, frozen world is the result of many years of work by scientists. It is thought that Pluto is made up of a mixture of rocks and several kinds of “ices”. Scientists believe that most of the ices that make up Pluto are frozen methane and ammonia.

What Is It Like on The Surface?
The surface of Pluto is very dark and extremely cold. Since the planet is so far away from the Sun, it gets almost no light or heat. Scientists believe that the temperature on the surface are less than -200 degrees Celsius. At this low temperature, almost everything freezes solid. Scientists believe that Pluto has a very thin atmosphere, but that it is far too thin to support any kind of life.

How Many Moons Does It Have?
Pluto has one tiny moon, named Charon, which wasn’t discovered until 1978. Charon is half the size of Pluto. No other moon in the solar system is as large, when compared to the planet it revolves around. Pluto and Charon are so similar in size that some astronomers think of them as a double planet.

Who discovered it?
Pluto was discovered in 1930 by the astronomer Clyde Tombaugh.

Does it have any special features?

  • After Neptune was discovered, astronomers noticed that something was changing the orbits of Uranus and Neptune. They decided that there must be another undiscovered planet that was causing these changes. Mr. Tombaugh spent a long time taking photographs of the area of the sky where the unknown planet should be and finally discovered Pluto in one of the photographs.
  • Pluto’s orbit is tilted. Looking at the solar system from an “edge”, most of the planets are in a line like a table top, with the Sun in the middle. This line, or plane, is called the ecliptic. The rest of the planets’ orbits stay on this plane. However, Pluto’s orbit is tilted at an angle to the rest of the solar system.
  • Pluto is another planet that spins around in the opposite direction from Earth. This means that the dim Sun would rise in the west and set in the east.

Resources Used
Astronomy for Kids
Small Worlds David Drew: Nelson, 1989
The Gas Giants David Drew: Nelson, 1989

Solar System Unit  |  Classification  |  Glossary

Images from: Astronomy Picture of the Day

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